<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="js/vue.js"></script>
</head>
<body>
    <div id="app">
        <p>{{ foo }}</p>
        <button v-on:click="foo = 'baz'">Change it</button>
    </div>

    <script>
        var obj = {
            foo: 'bar'
        }

        Object.freeze(obj)

        new Vue({
            el: '#app',
            data: obj
        })
    </script>

    
    
</body>
</html>